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Патент USA US2105641

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Jan. l8,v 1938.
F. H. DRAKE
2,105,641
AUTOMATIC VOLUME CONTROL CIRCUIT’
Filled May 5, 1935
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Patented Jan. 18, 1938
2,105,641
UNITED STATES PATENT OFFICE
2,105,641
AUTOMATIC VOLUME CONTROL CIRCUIT
Frederick H. Drake, Boonton, N. J., assignor to
Radio Corporation of America, a corporation of
Delaware
Application May 3, 1935, Serial No. 19,574
5 Claims. (01. 250—20)
My present invention relates to gain control itself, however, as to both its organization and
for radio receiving systems, and more particu
method of operation will best be understood by
larly to automatic gain control circuits for re
reference to the following description taken in
ceivers.
It is one of the main objects of my invention
to provide an automatic volume control arrange
ment for a receiver with low carrier level on the
detector, the control system utilizing a diode rec
ti?er provided by the cathode of ,an audio am
10 pli?er tube and a positive cold electrode thereof.
Another important object of the invention is
to provide an automatic gain control system for
a radio receiver of the type employing a carrier
ampli?er, a detector and an audio ampli?er, the
connection with the drawing in which I have
indicated diagrammatically several circuit or
ganizations whereby my invention may be car
ried into e?ect.
15 control system being characterized by the utili
zation of an output electrode and cathode of the
shown in Fig. 3,
Fig. 5 graphically illustrates the operation of
In the draWing:-—
Fig. 1 diagrammatically represents a receiving
circuit embodying the invention,
1O
Fig. 2 graphically ilustrates the Ip-Ep char
acteristic of the audio ampli?er in Fig. 1.
Fig. 3 shows a modi?cation of the invention,
Fig. 4 is a circuit analysis of the embodiment
audio ampli?er as the electrodes of a diode rec
the invention as shown in Fig. 1.
ti?er, and the audio tube cathode bias resistor
functioning to delay the gain control action.
Another object of this invention is to provide
Referring now to the accompanying drawing,
wherein like reference characters in the different
in a receiver an automatic gain control network
signal receiving system shown in Fig. 1 is of a
conventional type, and comprises a pair of tuned
which includes a carrier recti?er, the transmis
sion circuit feeding the carrier recti?er being
designed to suppress the ?ow of carrier energy
to the recti?er over a predetermined portion of
the receiver tuning range whereby automatic
gain control action is secured over a desired
portion of the tuning range, and is automatically
eliminated over a different portion of the said
range.
Another object of the present invention is to
?gures designate similar circuit elements, the
radio frequency ampli?ers l and 2 arranged in
cascade ahead of the detector tube 3. The de
tector is followed by an audio frequency ampli?er
tube 4, and the latter may be a tetrode of the
screen grid type. If the receiver is of the tuned
radio frequency ampli?er type, then the tuning
condensers 5, 6, and 1 may be uni-controlledly
arranged for simultaneous tuning of their re
spective stages. If the reeciver is of the super
provide an audio ampli?er tube network for a
heterodyne type, it will be obvious that the
radio receiver, the audio tube having its plate
stages I and 2 may represent the intermediate
3O
and cathode arranged to rectify the received ' frequency ampli?ers preceding the second de
35 signal carrier component of the detector output
tector 3. In any case each of the ampli?ers
circuit, the recti?ed carrier voltage being utilized
for varying the gain of the networks ahead of
l and 2 follow conventional construction, and the
circuits associated with tube | show a conven
the detector in a sense to maintain the carrier
tional type of tuned radio frequency ampli?er
circuit.
The ampli?er I includes the usual grid bias 40
intensity level at the detector input substan
40 tially constant despite carrier level variations at
the receiver input, and the audio ampli?er having
associated therewith balancing reactances for
minimizing effects due to the existence of audio
voltage between the plate and cathode of the
45 audio ampli?er,
Still other objects of the invention are to im
prove generally the simplicity and e?iciency of
automatic volume control systems for radio re
ceivers, and more especially to provide such con
50 trol systems so that they operate reliably, and
are readily constructed and assembled in a radio
receiver.
The novel features which I believe to be char
acteristic of my invention are set forth in par
55
ticularity in the appended claims, the invention
resistor 8 in its grounded cathode circuit, the
bias resistor being shunted by the customary
radio frequency by-pass condenser. The de
tector 3 is shown as being of the biased type,
and includes a biasing resistor 9 in its cathode
circuit, the resistor being shunted by a radio
and audio frequency by-pass condenser. The
plate circuit of the detector tube includes a
source of positive direct current potential B, the
latter being in series with a resistor l0 and the
primary winding ll of transformer T.
The low alternating potential side of winding
i! is connected to ground through a condenser
I2, and a radio frequency by~pass condenser I3 is
connected in shunt across the B voltage supply of 55
2
2,105,641
the detector stage. The audio ampli?er tube 4 has
its plate connected to ground through a path
which includes the secondary winding [4 of trans
former T and the resistor I5. The grounded
cathode circuit of tube 4 includes the usual
grid bias resistor IE3 shunted by a by-pass con
denser II. The signal input grid of tube 4 is con
nected to the junction of winding H and resistor
it through a path which includes condenser IB
and resistor It in series. The grid leak resistor
20 connects the grid side of condenser H! to the
ground side of resistor l6.-
s
A by-pass condenser 2! is connected between
the screen grid electrode of audio ampli?er 4 and
15 the plate side of resistorl?. The audio output
circuit of tube 4 includes the primary winding
of the audio transformer T1, the screen grid
electrode of tube 6 being connected to the high
alternating potential side of the transformer.
The low alternating potential side of the vprimary
winding of transformer T1 is connected by a lead
22 to the positive potential terminal of'source B.
The detector tube 3 serves as a radio frequency
ampli?er, as well as a detector, in order to get a
sufficiently high level for control on the diode
recti?er. If the transformer T is properly de
signed, as by coupled tuned circuits, the AVG
action may be obtained over a predetermined fre~
quency band without having control action over 10
the rest of the band. This is of advantage, for
example, in pursuit work of the Navy and Army
where communication with AVC is desired on one
end of the tuning dial, and homing work without
AVC is desired'on the other end of the dial. By 15
proper design of the network T, shown enclosed in
the dottedrectangle in Fig. 1, this transition‘ of
AVG action is automatically secured.
" Fig.5 shows graphically two illustrative char
A b r~pass condenser 23 is connected between the
screen, grid of tube 4 and ground. The secondary
ment, and eliminated over the remaining dial
winding of transformer T1. may be connected to
one, or more, additional stages of audio frequency
adjustment range. ‘The dotted line curve D 25
shows an. inverse charactertistic wherein AVC
ampli?cation, and the output of the final audio
ampli?er may be connected to any desired type of
of the dial range. Those skilled in the art will
The automatic volume control connection com
action is produced only over the latter portion
readily appreciate the constants and circuit ele
ments necessary to secure these characteristics 30
prises the lead 25 which is connected to the sig
in choosing the design of the network T.
nal input grid sides of the tuned input circuits of
example, the network T may be a low pass ?lter
the radio frequency ampli?ers of the receiving
network, and in such case the full line curve F
will be secured. If the network T is a high pass
?lter then the dotted line curve D is secured. If 35
desired the network T may be designed as a band
pass ?lter network, and in such case the charac
system. The lead 25 is designated by the letters
“AVC” to designate that it is the automatic
volume control path. A resistor-condenser net
work 26 is included in the AVG path, and func
tions to suppress the alternating current com
ponent of recti?ed carrier current. The AVC
lead 25 is connected to the plate side of resistor l5.
The detected output energy flows through two
paths to the network including tube 4. The audio
frequency component of the detected output cur
_ rent is transmitted through coupling network
45
above their normal operating negative biases.
acteristicswhich can be secured-by the proper 20
design of the network T. In the case of the full
line curve F the AVG bias is shown produced over
a substantial portion of the tuning dial adjust
reproducer.
30
and the grids of the controlled ampli?ers l and 2
have their negative biases increased over and
l0—|9—|8 to the control grid and cathode of
i the audio ampli?er, and the screen grid functions
as the audio output electrode of the ampli?er
tube 4. On the other hand the transformer T
functions as the transmission path for the car
50 rier frequency component of the detected cur
rent. The latter current is impressed between
the cathode and plate of tube 4, and the recti?ed
carrier voltage appears across resistor l5. In
other wordsthe cathode and plate of tube 4 co
55 operate to provide a diode recti?er, and. the recti
?ed voltage appearing across resistor I5 is em
ployed for varying the ampli?cation of the con
trolled ampli?ers ! and 2.
.It will be seen that since the grids of ampli?ers
60 l and 2 are connected to the plate side of re
sistor E5, the grids of the controlled ampli?ers
will become increasingly negative in bias as the
carrier intensity level increases. The AVC action
is delayed by virtue of the voltage developed across
65 the cathode bias resistor [6. In other words, the
bias resistor it not only functions to provide the
normal operating bias for the signal input grid
of audio ampli?er tube 4, but it also provides a
delayed negative bias, equal to the voltage de
veloped across resistor £6, for the plate of tube 4
with respect to the cathode. When the carrier in
For
teristic relating AVC' bias to tuning dial adjust
ment would have an intermediate portion of the
tuning dial adjustment range result in AVC 40
bias production.
The value of such an automatic switching ar
rangement resides in the fact that it is not nec
essary to employ any mechanical switches for
eliminating the automatic volume control action.
In homing work which covers from 200 to 1500
k, c., as when following a radio beacon, the AVG
action is detrimental, and is desired to be elimi
nated. The network T automatically suppresses
the transmission of carrier energy to the diode
recti?er when the carrier energy has a frequency
which isydisposed. in that portion of the tuning
range in which it is desired to suppress AVC
action. Pursuit command operation usually cov
ers a range of from 6200 to 7700 k. c., and AVC 55
operation is desired in this range.
Those skilled in the art are fully aware of the
manner of constructing a receiver. capable of
covering frequency ranges of 200 to 1500 k. c.;
and 6200 to ‘7700 k. 0. An all-wave receiver with 60
plug-in coils to cover these ranges would be used.
By winding transformer T to tune broadly through
the pursuit command range of 6200 to 7700 k. c.,
or some part thereof, no AVC action will be ob
tained at other frequencies. - The method of con
65
structing transformer T for this purpose will de
pend on the frequencies to be covered. Generally
speaking, the transformer will be wound to tune
roughly with the output capacity of the detector
and the plate capacity'of the audio tube; the 70
tensity peak voltage, impressed between the plate
primary and secondary windings being properly
and cathode of tube 4, exceeds the value of the
voltage developed across resistor I 6, then direct
75 current voltage is developed across resistor l5,
t‘eype using different I. F. values fordifferent
coupled. If the receiver is of the superheterodyne
bands, then the transformer T will be designed 75
2,105,641
to provide AVC action for all bands using a par
ticular I. F. value, and no AVC on other bands.
In Fig. 2 is shown the Ip-Ep characteristic of
audio ampli?er tube 4. Assuming a screen grid
voltage of 120 volts, the curve A designates the
variation of plate current with plate voltage.
For AVC action the positive plate current of the
shaded area S is utilized. It will be noted that
the positive plate current starts from zero plate
10 volts. With the constants employed a plate cur
3
a relatively wide range of signal frequencies, a
detector, means, responsive to variations in re
ceived signal carrier amplitude, for automatically
adjusting said ampli?er gain in a manner to
maintain the signal carrier amplitude at the de
tector input substantially uniform, said gain ad
justing means having a resonant input circuit,
and said last circuit being electrically constructed
to transmit all signal carrier energy of frequen
cies lying within a predetermined band of said
rent of 1 m. a. is secured with a peak plate voltage range and to reject signal carrier energy of fre
quencies lying within another band of the range
of 6 volts.
In Fig. 3 is shown an arrangement for balancing ' whereby said adjusting means is automatically
vout the eifect of audio voltage which may exist rendered inoperative when the tuning means is
adjusted to tune the receiver over said second 15
15 between the plate and cathode of the audio am
pli?er 4; by virtue of condenser 2! the screen may hand.
3. A method of receiving signals of a predeter
impress an audio potential on the plate. The
condenser E! is denoted by the symbol 0;; the mined frequency range which includes the steps
resistor I5 is denoted by the symbol R1, and the of amplifying the signals at radio frequency, de
bias resistor it is denoted by the symbol R2. A tecting the ampli?ed signals, amplifying the
condenser C2 is connected between the cathode audio component of detected signals, rectifying
side of resistor R2 and the screen grid electrode the carrier component of the detected signals,
varying the signal ampli?cation with direct cur
of tube 4.
In Fig. 4 there is shown a circuit analysis of rent voltage derived from the recti?ed carrier
component in a sense inverse to variations in the 25
the balancing arrangement of Fig. 3. The bal
received signal carrier amplitude, and automat
ancing arrangement of Fig. 3 is shown re-ar
ranged as a bridge arrangement, the resistors ically suppressing the transmission of said carrier
R1 and R2 being connected respectively between component for recti?cation during a predeter
plate and ground, and cathode and ground. The mined band of the said frequency range.
30 two other arms of the bridge comprise the con
denser C2 connected between cathode and screen,
and the condenser 01 eing connected between
screen and plate. An audio' voltage between
screen and ground, represented as a diagonal of
35 the bridge, will produce no effective voltage be
tween cathode and plate if the following relation
ship exists:
40
While I have indicated and described several
systems for carrying my invention into effect, it
will be apparent to one skilled in the art that my
invention is by no means limited to the particular
45
organizations shown and described, but that many
modi?cations may be made without departing
from the scope of my invention, as set forth in
the appended claims.
What I claim is:
1. A method of receiving signals of a prede
termined frequency range which includes the steps
of amplifying the signals at radio frequency, de
tecting the ampli?ed signals, amplifying the audio
component of detected signals, rectifying the car
rier
component of the detected signals, varying
55
the signal ampli?cation with direct current volt
age derived from the recti?ed carrier component
in a sense inverse to variations in the received
signal carrier amplitude, and automatically sup
60 pressing the transmission of said carrier com
ponent for recti?cation during a predetermined
portion of the said frequency range.
2. In combination, in a radio receiver, a signal
ampli?er provided with means for tuning it over
4. In a radio receiving system comprising a sig
30
nal ampli?er, a detector, an audio amplifier of the
screen grid type, means for impressing upon the
input electrodes of the audio ampli?er the audio
component of the detector output current, an
audio output circuit connected to the screen grid 35
of the audio ampli?er, a diode recti?er circuit
connected between the cathode and plate of the
audio ampli?er, means for transmitting to the
diode circuit the carrier component of the de
tector output current, a gain control connection 40
{between the diode circuit and the signal am
pli?er, and means for balancing out audio voltages
?existing between the cathode and plate of the
audio ampli?er.
5. In a radio receiving system comprising a sig 45
nal ampli?er, a detector, an audio ampli?er of the
screen grid type, means for impressing upon the
input electrodes of the audio ampli?er the audio
component of the detector output current, an
audio output circuit connected to the screen grid 50
of the audio ampli?er, a diode recti?er circuit
connected between the cathode and plate of the
audio ampli?er, means for transmitting to the
diode circuit the carrier component of the de
tector output current, a gain control connection 55
between the diode circuit and the signal am
pli?er, and said transmitting means having a
frequency transmission characteristic such that
said carrier transmission to- the diode circuit is
automatically prevented during at least one pre 60
determined portion of the receiver tuning spec
trum.
FREDERICK H. DRAKE.
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